1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. The present invention also relates to a process, a machine, a manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor device, a display device, a light-emitting device, a power storage device, a driving method thereof, or a manufacturing method thereof. In particular, the present invention relates to, for example, a power storage unit or a vehicle including the power storage unit. In particular, the present invention relates to, for example, a method for charging a power storage unit or a vehicle including the power storage unit. In particular, the present invention relates to, for example, a method for discharging a power storage unit or a vehicle including the power storage unit. The present invention relates to a power storage system. In particular, the present invention relates to, for example, a method for driving the power storage system.
Note that in this specification, the power storage unit is a collective term describing units and devices having a power storage function. Also in this specification, the electrochemical device is a collective term describing devices that can function using a power storage unit, a conductive layer, a resistor, a capacitor, and the like.
2. Description of the Related Art
In recent years, a variety of power storage units, for example, secondary batteries such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, have been actively developed. In particular, demand for lithium-ion secondary batteries with high output and high energy density has rapidly grown with the development of the semiconductor industry, for example, in the field of portable information terminals such as mobile phones, smartphones, and laptop computers; electrical appliances such as portable music players and digital cameras; medical equipment; and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs). The lithium-ion secondary batteries as rechargeable energy sources are thus essential for today's information society.
The performance required for the lithium-ion batteries includes increased energy density, improved cycle characteristics, safe operation under a variety of environments, and longer-term reliability.
An example of the lithium-ion battery includes at least a positive electrode, a negative electrode, and an electrolyte solution (Patent Document 1).